Chrysanthemum CmHSP90.5 as a Tool to Regulate Heat and Salt Stress Tolerance

Heat shock proteins (HSPs) play important roles in various stress conditions. In this study, CmHSP90.5, whose expression is induced by heat and salt, was cloned from a chrysanthemum (Chrysanthemum morifolium) 'Jinba' and expressed in Arabidopsis. We found that CmHSP90.5 localized in the chloroplast. The heterologous expression of CmHSP90.5 weakened the heat tolerance of Arabidopsis and reduced the activity of antioxidant enzymes, including superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX), indicating that CmHSP90.5-mediated heat stress sensitivity may be partially due to the regulation of active oxygen cleavage. The levels of expression of AtHSP101, AtHSP15.7, and AtHSP17.6C in CmHSP90.5-overexpressing plants decreased compared with those in wild-type (WT) plants under heat stress, indicating that these HSPs and CmHSP90.5 coregulate a plant's heat stress tolerance. In addition, the salt stress tolerance of the CmHSP90.5-overexpressing Arabidopsis decreased compared with that of WT plants; CmHSP90.5-overexpressing plants showed increased Na+ levels and decreased K+ and proline levels compared with those of WT plants. Interestingly, the expression of stress-related genes, such as the Na+/H+ antiporter encoding gene SOS1, high-affinity K+ transporter encoding gene HKT1;1, and proline synthesis gene AtP5CS1, decreased in CmHSP90.5-overexpressing plants under salt stress compared with those expressions in WT plants. Our findings lay a foundation for understanding the roles of CmHSP90.5 in response to abiotic stresses in chrysanthemum.